1. Field of the Invention
The present invention relates to an AC generator, and more particularly, to a vehicle AC generator that charges an in-vehicle battery and supplies an in-vehicle electric device with power.
2. Description of the Related Art
In a vehicle AC generator in the related art, as described in International Publication No. WO 2008-037294, a suction port of a fan provided to a bracket has a circular cross section. A diameter of the suction port decreases smoothly toward the fan and then gradually increases to a position adjacent to the fan in closest proximity.
In the vehicle AC generator in the related art, however, because the diameter of the suction port gradually increases toward the fan, a range in which momentum is given to the cooling air by the fan is reduced and so is an amount of pressure rise by the fan.
Consequently, even when a pressure loss at an outlet port side of the fan is lessened by providing a space at the tip end of the fan, the vehicle AC generator in the related art has a problem that an increase in air volume of cooling air decreases in a case where there is a certain amount of pressure loss in an air passage upstream of the fan.
Also, a pressure of airflow flowing out from the fan is high whereas a pressure is low in the vicinity of the suction port of the fan. Hence, a leakage flow of the cooling air is generated in a space in the vicinity of the tip end of the fan from downstream of the fan to the suction port of the fan. However, because the structure is such that the suction port of the fan gradually expands to the position adjacent to the fan in closest proximity, resistance against the leakage flow of the cooling air is so low that a flow rate of the leakage flow of the cooling air readily increases. Given that an amount of work by the fan is constant, an air volume of the discharged cooling air decreases when there is a considerable leakage flow of the cooling air.
[Patent Document 1] International Publication No. WO 2008/037294
As has been described, the vehicle AC generator in the related art described in Patent Document 1 has a problem that a temperature of a component that needs cooling by airflow generated by the fan rises due to a decrease in air volume of the cooling air.